package servlets;

/**
 * One Time pad encryption for user specific keys. <br>
 * <br>
 * This file is part of the Security Shepherd Project.
 *
 * <p>The Security Shepherd project is free software: you can redistribute it and/or modify it under
 * the terms of the GNU General Public License as published by the Free Software Foundation, either
 * version 3 of the License, or (at your option) any later version.<br>
 *
 * <p>The Security Shepherd project is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
 * PURPOSE. See the GNU General Public License for more details.<br>
 *
 * <p>You should have received a copy of the GNU General Public License along with the Security
 * Shepherd project. If not, see <http://www.gnu.org/licenses/>.
 *
 * @author Jason
 */
public class OneTimePad {

  private static final String KEY = "SuperKalaFragalisticExpeAloDocious";

  /**
   * Encrypts the supplied string value using the default key
   *
   * @param text The string that is to be encrypted
   * @return The resulting string from encryption
   */
  public static String encrypt(final String text) {
    return new String(
        org.apache.commons.codec.binary.Base64.encodeBase64String(xor(text.getBytes())).getBytes());
  }

  /**
   * Encrypts the supplied string value using the submitted key
   *
   * @param key The encryption key
   * @param text The string that is to be encrypted
   * @return The resulting string from encryption
   */
  public static String encrypt(final String text, String key) {
    return new String(
        org.apache.commons.codec.binary.Base64.encodeBase64String(xor(text.getBytes(), key))
            .getBytes());
  }

  /**
   * Decrypts the supplied string value using the default key
   *
   * @param hash The cipher text to be decrypted
   * @return The plain text revealed from the decryption
   */
  public static String decrypt(String hash) {
    try {
      return new String(
          xor(org.apache.commons.codec.binary.Base64.decodeBase64(hash.getBytes())), "UTF-8");
    } catch (java.io.UnsupportedEncodingException ex) {
      throw new IllegalStateException(ex);
    }
  }

  /**
   * Decrypts the supplied string value using the submitted key
   *
   * @param hash The cipher text to be decrypted
   * @param key The encryption key
   * @return The plain text revealed from the decryption
   */
  public static String decrypt(String hash, String key) {
    try {
      return new String(
          xor(org.apache.commons.codec.binary.Base64.decodeBase64(hash.getBytes()), key), "UTF-8");
    } catch (java.io.UnsupportedEncodingException ex) {
      throw new IllegalStateException(ex);
    }
  }

  /**
   * XOR Function
   *
   * @param input Byte array to be XOR'd
   * @return
   */
  private static byte[] xor(final byte[] input) {
    final byte[] output = new byte[input.length];
    final byte[] secret = KEY.getBytes();
    int spos = 0;
    for (int pos = 0; pos < input.length; pos += 1) {
      output[pos] = (byte) (input[pos] ^ secret[spos]);
      spos += 1;
      if (spos >= secret.length) {
        spos = 0;
      }
    }
    return output;
  }

  /**
   * XOR Function
   *
   * @param input Byte array to be XOR'd
   * @param key Encryption Key
   * @return
   */
  private static byte[] xor(final byte[] input, String theKey) {
    final byte[] output = new byte[input.length];
    final byte[] secret = theKey.getBytes();
    int spos = 0;
    for (int pos = 0; pos < input.length; pos += 1) {
      output[pos] = (byte) (input[pos] ^ secret[spos]);
      spos += 1;
      if (spos >= secret.length) {
        spos = 0;
      }
    }
    return output;
  }
}
